1. Field of Invention
The invention relates to a hard tile having a support layer and a wearing layer and to a covering surface comprising such tiles. Nowadays, very high demands in terms of mechanical strength, resistance to wear and resistance to chemicals are imposed on covering surfaces made from plastics. Moreover, such coverings should not undergo any electrostatic charging or should at most undergo extremely slight electrostatic charging.
2. Description of Related Art
European Patent EP-A 1 128 713 discloses tiles made from highly compressed thermoplastic with a nonconductive support layer and a conductive wearing layer. A wearing surface of the wearing layer is provided with a securely adhering conductive substance. The tiles described in that document have connecting elements in tongue-and-groove form. Only specialist workers can lay tiles of this type. The tongue-and-groove connection often tears, and in addition the tiles are complicated and expensive to produce.
Tiles for floor coverings are generally secured to one another by means of plug connections. The joints which are present between the individual tiles are susceptible to dust and dirt. This can lead to the projections curving upward over the course of time. This makes the floor covering more difficult to drive on and reduces its service life, which is undesirable for economic and ecological reasons.
Therefore, it is an object of the present invention to provide a hard tile which is configured in such a way that it is easy to lay.
A further object of the present invention is to provide a covering surface which is produced using tiles which are easy to lay and which has a long service life.
The wearing layer of the tile according to the invention is polygonal in shape and is preferably square or hexagonal. The wearing layer does not have either cutouts or projections. After the tiles according to the invention have been laid, neither cutouts nor projections are visible from above, since the tiles are mechanically secured by the support layer. The floor covering has narrow joints between the individual tiles. The regular, preferably square pattern of these joints also allows simple welding, so that it is impossible for any dirt to adversely affect the floor covering. The wearing layer is preferably electrically conductive.
The support layer of the tile according to the invention is of substantially the same size as the wearing layer and is preferably likewise polygonal. In its edge regions, the support layer has projections and mating cutouts. The edge region of the support layer has a width which corresponds to the length of the cutouts and projections. The projections are intended to engage in a positively locking manner in the cutouts in adjacent tiles.
In one embodiment, the intermediate layer extends over at least two adjacent edge regions of the support layer and at least two further edge regions of the support layer are free of the intermediate layer. When the tiles according to the invention are being laid, this leads to those projections on the edge regions of the support layer over which the intermediate layer extends engaging in those cutouts in the edge regions of the support layer which are free of the intermediate layer. As a result, a covering which is produced using the tiles according to the invention has a continuous intermediate layer, ensuring electrical conductivity over the entire area. Since the location of the mechanical connection is not at precisely the same point as the electrical connection, this means that slight local shifts in adjacent tiles do not lead to an interruption in the conductivity, and therefore there is a high degree of reliability with regard to the electrical conductivity.
In a further embodiment, the intermediate layer extends over at least two adjacent edge regions of the support layer and over the projections of the support layer of two further adjacent edge regions. The result of this is that the intermediate layer is doubled up in those regions in which the tiles are secured to one another. Therefore, a floor covering produced in this way satisfies the high demands imposed with regard to the electrical conductivity.
The tiles according to the invention can even be laid on uneven subfloors without the dissipation of the electrostatic charges being adversely affected. The tiles according to the invention are laid without a fixed joint to the subfloor.
Production of the tiles according to the invention is very advantageous, since only the wearing layer has to satisfy the particular demands with regard to the electrical conductivity, the resistance to wear and the resistance to aggressive chemicals. The intermediate layer has to be electrically conductive.
Depending on requirements, inexpensive materials, such as for example reclaimed materials, can be used for the support layer.
The wearing layer of the tile according to the invention is preferably made from thermoplastic particles, generally chips, which are provided with a conductive coating before being pressed. During the pressing at elevated temperature, the plastic particles are subjected to considerable deformation together with the conductive coating, resulting in a homogeneous block which has uniformly distributed, thin conductive layers passing through it. In a particularly preferred embodiment, the wearing layer has a grid printed on its underside, increasing the conductivity between wearing layer and intermediate layer (cf. also EP 0 869 217).
It is particularly advantageous for the projections to have a dovetail-like shape, since this makes the laying of the tiles to form a covering surface and also dismantling of such a covering surface particularly simple without the electrical conductivity between the tiles being adversely affected. The dovetail-like cutouts may be either polygonal or undercut. In one embodiment, narrow and wide projections and undercuts alternate at regular intervals. The shape and width of the dovetails can be matched to the demands of the particular application; in particular, appropriate attention must be paid to the radii.
The electrical charging is preferably dissipated via the edges of the covering surface produced using the tiles according to the invention.
The intermediate layer of the tiles according to the invention is an electrically conductive sheet-like structure. This may, for example, be a metal grid, a pattern of conductive fabric or copper strips, but may also be a conductive film or a conductive coating layer. Polystyrene films with added carbon black and soft polyvinyl chloride films with added carbon black are particularly preferred.
In a further embodiment, the load-bearing capacity of the support layer is increased if the support layer has compression elasticity properties. By way of example, the support layer may be at least half made up of a polygonal structure, such as a honeycomb structure. The recesses in the edge regions of the polygonal structures improve the ventilation of the subfloor, which is preferable in particular in moist environments. The tile according to the invention is preferably produced in such a way that the intermediate layer is applied to the wearing layer which has been laid down. This can be effected either by applying the film or by applying a coating. In a final step, the support layer is applied, preferably by means of injection molding, to the intermediate layer which has been applied to the wearing layer.